What is this line in the middle of my blender screen?
(from the manual)

&quot;The Origin of an Object is shown in the 3D view by a small orange circle.
While the Origin is equivalent to the center of the Object, it does not have to be located in the center of the Mesh. This means that an Object can have its center located on one end of the mesh or even completely outside the mesh.&quot;

That dotted line means that an object is parented to other object.

&quot;Moving, rotating or scaling the parent will also usually move/rotate/scale the child/children. However moving/rotating/scaling the child/children of the parent will not result in the parent moving/rotating/scaling. In other words, the direction of influence is from parent to child and not child to parent.&quot;

Read this: https://www.blender.org/manual/modeling/objects/groups_and_parenting.html